Describe what the following MATLAB code does. The original function name has been replaced by XXX.

clc;

clear all;

close all;

[filename, pathname, filterindex] = uigetfile( ...

{ '*.jpg','JPEG (*.jpg)'; ...

'*.bmp','Windows Bitmap (*.bmp)'; ...

'*.fig','Figures (*.fig)'; ...

'*.*', 'All Files (*.*)'}, ...

'Choose image(s) to be processed', ...

'MultiSelect', 'off');

if filterindex==0, break;end

filename=cellstr(filename);

im2= imread(horzcat(pathname,char(filename)));

im1=rgb2gray(im2);

im3=im2double(im1);

[n,m]=size(im3);

c1=0;

h = waitbar(0,'Calculating XXX please wait......');

k=1;l=1;

for l=0:1:m-1

for k=0:1:n-1

for x=0:1:n-1

for y=0:1:m-1

a=x+1;b=y+1;

c= im3(a,b) * exp(-1i*2*pi*(k*x/n + l*y/m));

c1=c1+c;

end

end

aa=l+1;bb=k+1;

im(bb,aa)=c1;

c1=0;

end

waitbar(l / m);

end

ims = im*255;

close(h)

imshow(ims);title('XXX plot');

figure

imshow(log(abs(ims)),[-1 5]); colormap(jet); colorbar;title('absolute value of XXX plot');